Low molecular weight polyuronic acids, because of their high affinity for magnesium and calcium ions, are expected to have utility as scale inhibitors and scale deposit removers. They are also expected to have utility as detergent builders. The biodegradability of polyuronic acids makes them particularly valuable with respect to environmental acceptability and waste disposal. Two types of low molecular weight polyuronic acids, polyguluronic acid and polymannuronic acid, have been shown to exhibit root growth promoting activity in barley (M. Natsume et al., “Isolation and Characterization of Alginate-derived Oligosaccharides with Root-Growth Promoting Activities,” Carbohydrate Research, 258, 187-197 (1994)). A mixture of low molecular weight polyuronic acids, having an average molecular weight of 1800 g/mole, has been shown to promote germination and shoot elongation of unhulled rice, Komatsuna seeds, and tobacco callus (Y. Yonemoto et al., “Promotion of Germination and Shoot Elongation of Some Plants by Alginate Oligomers Prepared with Bacterial Alginate Lyase,” Journal of Fermentation and Bioengineering, 75, 68-70 (1993)). Another type of low molecular weight polyuronic acid, polygalacturonic acid, has been shown to exhibit murine immunomodulating activities, including mitogenicity, adjuvanticity, interferon-inducing activity, macrophage-activation activity, and antitumor activity (Y. Kumazawa, K. Mizunoe, and Y. Otsuka, “Immunostimulating Polysaccharide Separated from Hot Water Extract of Angelic Acutiloba Kitagawa Yamato Tohki,” Immunology, 47, 75-83 (1982)). Low molecular weight polygalacturonic acid also has been shown to exhibit plant-defense stimulating activity (E. A. Nothnagel, M. McNeil, P. Albersheim, and A. Dell, “Host-Pathogen Interactions XXII. A Galacturonic Acid oligosaccharide from Plant Cell Walls Elicits Phytoalexins,” Plant Physiology, 71, 916-926 (1983)). Furthermore, uronic acid derivatives, in which a hydrophobic polymer is covalently attached to the reducing terminus of the polyuronic acid, are useful as dispersants in pigment dispersed aqueous ink compositions for use in ink jet printing.
Hydrolytic methods, although available for obtaining low molecular weight polyuronic acids from high molecular weight polyuronic acids, are typically unselective and require considerably long reaction times. Examples include (1) the method disclosed in A. Haug et al., “Studies on the Sequence of Uronic Acid Residues in Alginic Acid,” Acta Chemica Scandinavica, 21, 691-704 (1967); (2) the method described in R. Kohn, “The Activity of Calcium Ions in Aqueous Solutions of the Lower Calcium Oligogalacturonates,” Carbohydrate Research, 20, 351-356 (1971); and (3) the method disclosed in European Patent Application EP 0 487 340 A1, “Coating for Food Composition Limiting Fat Absorption upon Frying.”
Oxidative degradation of high molecular weight polyuronic acids has been reported using (1) hydrogen peroxide only and (2) hydrogen peroxide and an iron salt (Fenton's reagent). As an example of the former method is GB 1,250,516, in which salts of alginic acid, a high-molecular weight polyuronic acid, are oxidatively degraded to lower molecular weight products. By this method, a fifteen weight percent solution of the degraded alginic acid product is described to have a viscosity in the range of 10 to 50 centipoise at 20° C., a range significantly higher than that of the product polyuronic acids of the present invention.
The earliest reported oxidative degradation of high molecular weight polyuronic acids using hydrogen peroxide and an iron salt (Fenton's reagent) is in V. H. von Euler et al., “Oxidative Decarboxylation of Pectin, Diketogulonic Acid and Pyruvic Acid” Makromol. Chem, 18/19, 375-382 (1956). In that report, a pronounced decrease in the viscosity of a 0.3 wt. % solution of pectin, a complex high-molecular weight polyuronic acid, after treatment with hydrogen peroxide and ferric chloride, is reported. Galactose and carbon dioxide are reported as decomposition products. There is no indication in that report that other degradation products, different from those described, could be obtained. Additionally, there is no indication that the degradation reaction, carried out under conditions different from those described, could yield one or more valuable degradation products in reasonable yields. Specifically, there is no indication that polyuronic acids, having an average degree of polymerization less than 20, could be obtained in reasonable yields.
The next earliest reported oxidative degradation of high molecular weight polyuronic acids using hydrogen peroxide and an iron salt (Fenton's reagent) is in P. S. O'Colla et al., “The Action of Fenton's Reagent on Acidic Polysaccharides,” Proceedings of the Chemical Society, 68-69, 1962. In that report, the degradation of a uronic-acid containing disaccharide and uronic-acid containing polysaccharides by aqueous hydrogen peroxide and ferric acetate is reported. 6-glucuronosyl-D-galactose, a uronic-acid containing disaccharide, is reported to be degraded to simple sugar products. Gum arabic, a complex high-molecular weight uronic-acid containing polysaccharide, is reported to be degraded to four low-molecular, dialyzable products. Three of these dialyzable products were characterized and identified as the simple sugars, galactose, arabinose, and rhamnose. The fourth dialyzable product was an unidentified disaccharide. Sodium alginate is reported to be degraded rapidly to unidentified low-molecular, dialyzable products. There is no indication in that report that degradation products, other than simple sugars or disaccharides, could be obtained. Additionally, there is no indication that the degradation reaction, carried out under conditions different from those described, could yield one or more valuable degradation product in reasonable yields. Specifically, there is no indication that polyuronic acids, having an average degree of polymerization less than 20, could be obtained in reasonable yields.
A third reported oxidative degradation of high molecular weight polyuronic acids using hydrogen peroxide and an iron salt (Fenton's reagent) is in O. Smidsrod et al., “Kinetic Studies on the Degradation of Alginic Acid by Hydrogen Peroxide in the Presence of Iron Salts,” Acta Chemica Scandinavica, 19, 143-152 (1965). In that report, an investigation of the oxidative degradation of a 0.3 wt. % solution of sodium alginate by aqueous hydrogen peroxide and ferric chloride hexahydrate using viscosimetric and titrimetric methods is reported. For the restricted case in which only 0.1-1% of the bonds in the alginate polysaccharide are broken, the rate of alginate degradation is in good agreement with theory by J. Weiss (Advan. Catalysis 4, 31, 1952). According to that theory, hydroxyl radical attack on the substrate is implicated which may be described by the following equation: Alginate+OH.→ Products. In both this work by O. Smidsrod et al. and in earlier work (“Degradation of Alginate in the Presence of Reducing Compounds,” Acta Chemica Scandinavica, 17, 2628-2637, 1963), none of the products of the degradation were characterized or identified. There is no indication in these reports that valuable degradation products could be obtained. Additionally, there is no indication that the degradation reaction, carried out under conditions different from those described, could yield one or more valuable degradation product in reasonable yields. Specifically, there is no indication that polyuronic acids, having an average degree of polymerization less than 20, could be obtained in reasonable yields.
Thus, there remains a need for a method of manufacturing polyuronic acids, having an average degree of polymerization less than 20, which may be carried out on an industrial scale. Specifically, there remains a need for a process in which relatively concentrated solutions and/or mixtures of starting materials, reactants, and products may be used. Additionally, there remains a need for a process in which relatively cheap reagents are used. Additionally, there remains a need for a process in which the reactions and/or processing steps are fast and simple.